The Coast Guard commandant warned that his service’s presence in the Arctic may not be enough to ward off Chinese and Russian encroachment unless the U.S. signs the United Nations Convention on the Law of the Sea – and that even if the U.S. signed the treaty now, it might be too little, too late.

The U.S. Coast Guard has begun work to design and buy three heavy and three medium polar icebreakers, but the service reserves the right to increase the size of the program or even add offensive weapons to them if needed to respond to a rapidly changing Arctic environment, the commandant said.

The U.S. Navy’s presence in the Arctic region has been limited due to constrained budgets and urgent needs elsewhere in the world, the chief of naval operations said, but future ships should still be designed with potential Arctic operations in mind.

China has made clear that it refuses to accept an international arbitration panel’s ruling against its territorial claims in the South China Sea, but whether that stance leads to increased military tensions between Beijing and the United States or opens the door for broader negotiations is an open question.

The U.S. Coast Guard has determined — through independent analysis — it needs three heavy and three medium icebreakers to cover the U.S. anticipated needs in the Arctic and Antarctic, commandant Adm. Paul Zukunft, told reporters on Tuesday.